Method of adding flotation reagents in froth flotation processes



Aprll 14, MASAYOSH] w ET AL METHOD OF ADDING FLOTATION REAGENTS IN FROTH FLOTATION PROCESSES Filed Nov. 25, 1968 I I l I 4 23 l6 v v 23 I 25 1-; r

I5 I i 27 SOURCE OF GAS I2 INVENTORS MASAYOSl-H WADA AKIRA OHBA GORO ISHII SHUZO KOHNO ATTORNEYS United States Patent Int. Cl. B0311 1/02, 1/20; B03b 1/04 US. Cl. 209166 1 Claim ABSTRACT OF THE DISCLOSURE Method of adding flotation reagents in a froth flotation process by feeding the reagents as an Aerosol or in finely divided form into the air or other gas supplied as primary gas through an injecting system into the essential zone of bubble dispersion and bubble-particle contact of the flotation apparatus.

This application is a continuationin-part of application Ser. No. 608,289 filed Jan. 10, 1967, now abandone'd.

BACKGROUND OF THE INVENTION Field of invention and prior art The present invention relates to an improvement in froth flotation of sulfide ores, oxide ores and other ores, and raw material and other materials. There is an increasing field of application for froth flotation, such as to the treatment of low grade ores, complex ores and types of ores which are diflicult to extract. However, in the existing flotation method there exist various problems such as lowering of the floatability when ore particles are finely pulverized, the undesirable effect of slime, surface oxidation of the ore particles and the effect of soluble salts, increased reagent consumption encountered with increasing fineness of particulate ore and with the complexity of the structure of the ore, and lack of sufliciently selective reagents. Since the solution of these problems is quite diflicult, the complete refining of mineral ores has not been attained.

SUMMARY OF THE INVENTION The inventors of the present invention, after cumulative studies carried out on the thermodynamics of the flotation reaction, have established a basic flotation theory of the contact mechanism of the froth and particles, and the inventors have devised a new flotation method based on this theory which utilized gas phase adsorption.

The method of the present invention achieves the greatest flotational effect by thermodynamic promotion of the contact of froth and particulate ore or mineral, and the method involves introduction of gas into the flotation system so as to produce bubbles in the system, and prior to its introduction the addition of an aqueous solution of flotation reagents including a frothing agent and a collecting and/or other flotation reagent into the gas as an Aerosol in extremely finely dispersed form in order to provide prior and positive adsorption of the reagents onto the gas-liquid interface of the gas bubbles and preferential adsorption of the reagents onto the solid-gas interface of the ore particles in contact with the froth.

3,506,120 Patented Apr. 14, 1970 BRIEF DESCRIPTION OF THE FIGURE The figure is a cross-sectional view of a froth flotation apparatus having means to introduce the flotation reagents according to the method of the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT In considering the contact between the froth and the ore particles, the work done by the contact can be expressed by the equation of Dupre and Young as follows:

Where AW AW, and A8 are the variations of the work of contact from their standard conditions for respective solid-gas, gas-liquid and solid-liquid interfaces.

The above equation indicates that the value of AW should be increased for a given value of AW namely, the change in work during the contact between the froth and a particle, by a decreased in the values of both AW and AW namely, the change in work done during the contact between froth and liquid and the change in work during the contact between a particle and the liquid, respectively.

However, a minimum value of AW is required for the dispersion of froth, and thus it becomes necessary to keep the value of AW as small as possible in order to make the value of AW large.

In the existing flotation methods, because the frother, collector and all other reagents are added in solution to be adsorbed into the gas-liquid interface of the froth and onto the solid liquid interface between the liquid and the particles of the ore, it is difficult to obtain a low value of AW and a high value of AW in conditioning and flotation periods.

In the present invention, the frother, collector and other reagents in an aqueous solution are added to the gas and thus the added reagents are adsorbed onto the gas-liquid interface of the froth and onto the solid-gas interface between the gas and the particles of ore, and this causes the value of AW to be as small as possible, easily enabling an increase in the value of AW In the gas-phase adsorption process the reagents having lower free surface energies per unit area will tend to concentrate on the liquid surface. This does not, however, result in the complete replacement of the surface solvent molecules by the solute molecules owing to the diffusion of the latter into the solution.

The diffusion of the solute molecules depends upon the concentration gradient between the bulk of the solution and the surface layer and the degree of thermal agitation and attraction of molecules. For a solute of higher molecular weight the attainment of the equilibrium is almost instantaneous even at a very low pressure of the solute in the gas phase owing to the slow rate of diffusion of the surface solute molecules into the bulk of the solution.

For constant temperature and pressure, the relationship between the surface free energy and the surface concentration of the solute is given by the Gibbs equation where ti is the infinitesimal change of the chemical potential of the solute z and is the excess number of moles of the solute per unit area of the gas-liquid interface.

the chemical po-' the Gibbs of one mole of the solute in the pure state depending on temperature and pressure, R the gas constant and T the absolute temperature.

From these relationships, it is clear that the large specific surface area of the finely dispersed bubbles loaded with the solution favors the gas-phase adsorption process and a minimal amounteof the solute can be added.

The. attachment of gas bubbles to solid particles depends upon the surface free energy changes and the stability of V the hydrated layers surrounding both the bubbles and the particles on contact.

The hydration of solid surfaces occurs as the result of free, atomic and molecular forces in the surface of the crystalline lattice attracting dipoles of liquid and of the adsorption of hydrated ions .on the surface. The polar groups of the molecules adsorbed at gas bubble surfaces are also hydrated. g

In the zone of the three-phase perimeter of;;wetting the dewetting of solid surface EPIOCCfidSWhEIl the hydrated layer on thesolid surface is replaced by the gas or ,the solute having diphillic or nonpolar structure:

In differentiating Youngs equation (5) where s and 'y are respective interfacial energies and 0 the contact angle, and combining with the Gibbs equation, we obtain where I i F5 and I? 7 are the excess number of moles of the solute 1' per unit area of the solid-gas and solid-liquid interfaces respectively.

It is seen from Equation 6that for the decrease in the value of cos or the increase in the value of 0 the following conditions must be satisfied: For O 0 1r/ 2 for 1r/2 0 1r 2 re t. Z, i m co e 2 M! and for 0=1r2 2 i m 2 i m The above conditions suggest conclusively the possibility of the gas-phase adsorption process in the threephase contact.

For example, let us consider a simple system of nitrogen gas, collector and water as components. For constant temperature and pressure, the Gibbs equation in the form 7" ltxunx' 15 l 'H o un, (19) is valid for the solid-gas interface and that in the form 'Yal iix' uax i'hg H O (1 1) for the solid-liquid interface since the adsorption of nitrogen gas at the solid-liquid interface may be neglected,

4 7 where dy is the infinitesimal change of the free energy of the solid-gas interface in the gas-adsorption system,

are the excess number of moles of 'collector, water and nitrogen gas at the solid-gas interface, and

Fax. and 1&

are the excess number of moles of, collector and water at the solid-liquid interface respectively in the same system.

In combining the Gibbs-Duhem equations for the bulk phases For the contact angle to .increase with increasing concentration of the collector in the gaseosu phase, the sum in the brackets of the right-hand side .must be positive or it must be established that the collector adsorption ii x- COS iix' and the water adsorption s1 HgO IS]:%2O and mix Prr o Pnx' 2 z z or the adsorption density of nitrogen gas at the solid gas interface is negligibly small.

Equation 15 shows that the adsorption density of collector at the solid-liquid interface must be as small as possible and the adsorption'density of collector at the liquid-gas interface must be smaller for the contact angle between 0 and 11/2 and larger for the contact angle between n/2 and nfiThe adsorption density of the collector may be controlled by varying that of frother which when introduced into the gas phase adsorbs preferentially at the liquid-gas interface.

Equation 17 requires that the partial pressure of the collector in the gas phase must be kept low when the adsorption density of nitrogen gas at the solid-gas interface is not negligibly small. It is shown from the equation that the collector should be added as an aqueous solution into the gaseous phase.

From Equation 16 it is clear that the adsorption, density of water or the degree of hydration at the solid-liquid interface must be higher than that of the solid-gas interface.

From these considerations follows that the liquidphase adsorption process can hardly be regarded as a reasonable process. In the liquid-phase adsorption process, the solid surface adsorbs collector from the liquid phase at the conditioning stage and has a large value of the adsorption density of the collector and a small value of the adsorption density of water at the solid-liquid interface. Since the above conditions of the three-phase contact must be fulfilled at equilibrium, thevflotation time must be prolonged unless some othereffects are operative in favor of the bubble-solid attachement.

.As shown in the figure, a flotation apparatus comprises an open top container 10 having a hollow central column 11 extending downwardly into it, the column 11 having an inverted cone 12 at the bottom thereof, the lower edge of which is spaced from the bottom of the container. Extending down through the hollow column 12 is a rotatable shaft 13 driven by a motor (not shown) and having an agitator impeller 14 on the lower end thereof, which impeller is below the lower edge of the inverted cone 12. Swirl plates 19 are provided around the impeller 14. Opening into the cone is a primary gas inlet 15, and at the upper end of the column 11 is a secondary gas inlet 16. Connected to the primary gas inlet is at least one, and preferably a plurality of Aerosol forming devices, each comprised of a container 23 containing an aqueous solution 24 of flotation reagents and an atomizer device 25, the gas supply conduit 26 of which is connected to a supply of gas under pressure indicated schematically at 27. Valved conduits 22 connect the containers 23 to the primary gas inlet.

In operation, the gas under pressure from the source 27 has the flotation reagents introduced into it either as Aerosols, or the flotation reagents in aqueous solution are atomized, preferably to an Aerosol, by a jet of the compressed gas in the atomizer device 25. The gas thus charged with the flotation reagents is added to the flotation system through the primary gas inlet 15 as the agitator impeller 14 is rotating in the liquid phase of the system. The agitation of the impeller is such as to pump liquid with gas entrained therein beneath the edge of the cone 12, and in the outer portion of the container, the bubbles of gas thus formed will rise to the surface as the froth. The raw material to be treated is introduced into the system through column 11 while secondary gas, usual- 1y air, is entrained therein through secondary gas inlet 16 in a manner which ensures intimate contact of the froth in a nascent state and the ore pulp in flow.

The gas charged with the reagent in aqueous solution is preferably being fed into the eye of the impeller, since the gas entrained by the pulp flowing through the impeller blades will be broken up into smaller bubbles by the rapid acceleration at the center and the prevailing turbulent flow at the periphery of the impeller.

As a practical matter, the gas used for the primary gas can be air, such as from a compressor, or nitrogen, oxygen, hydrogen, carbon dioxide, sulphur dioxide, or the like, from a supply of compressed gas. The pressure should be about 2 kg./cm. or more, depending on the conditions in the particular apparatus. The reagents should be added as an aqueous solution, the concentration of which depends upon the viscosity, surface tension and density of the reagents. The degree of dispersion of the reagents in the primary gas can be varied to suit the conditions in the flotation system by varying the concentration of the reagents in aqueous solution, the partial pressure of gas or water vapor in froth, the gas pressure, the size of the dispersing nozzle, etc.

The present invention results in significant improvements over conventional froth flotation methods as follows:

(1) Because the frother is adsorbed onto the gas liquid interface of the froth from gas phase directly and instantaneously, many finely dispersed froths can be evolved quickly while introducing a constant amount of gas or air into the flotation system.

(2) The method of the invention allows instantaneous or continuous control of both dispersion of the gas into the ore pulp to form the froth and the addition of the reagents. The flotation process can thus be operated at the optimal flotation condition for the particulate ore being treated, thereby enabling automation of the process.

(3) Flotation velocity, i.e., the rate at which the ore particles are picked up in the froth, is increased, with a consequent increase in the capacity of the flotation apparatus.

(4) Because of the ease of froth dispersion and the increase in flotation velocity, the power required for flotation apparatus can be reduced and abrasion of the parts of the apparatus is also reduced.

(5) Since the intensity of agitation of the pulp can be reduced because of the ease of froth dispersion, the separation of particular ore becomes favorable and this prevents excessive formation of secondary slime.

(6) The stability of the froth in the foam layer is increased, which in turn accelerates ore-selection action.

(7) Because the collecting agent is adsorbed directly onto the solid-gas interface rather than on the solid-liquid interface of the ore particles, the ore particles have maximum: floatability.

(8) Direct adsorption of collector reagent from the gas phase onto the surface of ore particles makes it possible to utilize the different adsorption rates of various minerals to achieve selective separation of the particles of ore.

(9) The difference in flotation velocity of the particles of the different ore constituents can, because of the increased overall flotation velocity, be better utilized fOll separation of the ore constituents.

(1 0) The amounts of collector, frother and other reagents can be kept to a minimum.

The present invention will be further illustrated by several examples.

EXAMPLE 1 A complex sulfide ore having 0.4 percent copper, 2.5 percent lead, 7.2 percent zinc and 14.4 percent iron (FeS was pulverized in a wet type ball mill to a size of approximately percent under-4 0 0 mesh, and this was treated in an apparatus shown in FIG. 1. The container could float 500 g. samples of mineral for batch testing, and was made of polyethylene and of 2,500 cm. in volume. The impeller 14 was made of stainless steel and was 58 mm. in diameter and had a disk with four blades, inclined 60 to the horizontal and 13 mm. in vertical height. The drive was by a directly connected motor of w. and of 1,500 rev/min. Twenty swirl plates 19 made of stainless steel, 17 mm. in width and 30 mm. in height, were equally spaced at angles of 45 with a tangent to the periphery of the supporting ring.

The air or gas containing reagents as Aerosols was introduced a tubing 15, which was 9 mm. in inner diameter. The gas was air from a diaphragm type rotary compressor, operating at 2 rkg/cm. pressure and producing about 12 l./min. of compressed air. The secondary gas was air sucked into the column 11 through the two openings 16 which were each 10 mm. in diameter and equipped with an adjusting ring with corresponding openings and located at the upper end of the column 11. The rate of air supply was kept constant, being 7.3 l./min. for the primary air and 25 l./min. for the secondary air.

The dispersion of the reagents into the primary gas was obtained by an Aerosol producer depending for its action upon a sudden and violent collision between a jet of the liquid or the solution of reagents and a jet of the compressed air in an enclosed vessel connected between the feed pipe 15 and the compressor. The flotation conditions were as shown in Table I, and produced the results as shown in Table II.

TABLE IL-RESULTS OF FLO'IATION Assay (percent)Method of the present invention Recovery (percent) Product Cu Pb Zn Fe(FeS2) Cu Pb Zn I e(FeSz) Concentrate 0.72 3. 75 8.13 12. 45 97. 9 87. 4 62. 4 49. 1 Tailing 0. 02 o. as s. 18 16.27 2. 1 12.6 37. e 50. 9

O onventional method t t 0.96 4. 95 9.15 12.46 96.0 92.8 57.5 37.2 T355525? 0.03 0.29 5.13 15.93 4.0 7.2 42.5 62.8

EXAMPLE 2 TABLE V Compound sulphide ores containing Cu0.4%, Pb'-- Rate of effective gain Percent 2.4%, Zn711%, and FeS 15.6% and crushed by a Cu 93.7 ball mill wet type crusher into fine grains 98% of which Pb 60.5 were a size less than 400 mesh was the material used for Zn 40.4 the flotation, and a water pulp was prepared having a Fe(FeS 28.8 concentration of 25 temperature of 26 C. (ambient), EXAMPLE 5 and pH 7.7 (neutral). A 1% water solution of a rein- 20 forcing agent, ethyl-xanthogenic acid natrium (hereinafter referred to as NaEX) was placed in one container 23 in the drawing, and a 1% water solution of a bubbling agent, methyl-isobutyl-carbinol (hereinafter referred to as MIBC) was placed in the other container, and both were atomized with compressed air. A quantity corresponding to 1.25 g./t. of NaEX was first added to the pulp and then a like amount of MIBC as Aerosol. After performing flotation for three minutes, as shown in Table III both the quantity of floating ores and the rate of effective gain were far greater and the floating property of the ore grains was greatly increased as compared with the flotation, in which 1.25 g./t. of 1% water solution of each of NaEX and MIBC was respectively added as a Water solution to the ore grain pulp.

The flotation was performed again under the same condition as in Example 2 above, except that the quantity of NaEX and MIBC was changed until the rate of effective gain reached the range of 95-96% Where the quantity of the reagent was measured. The results compared with the ordinary case was as follows:

TABLE IV NaEX g./t. MIBC g./t.

This method 1. 25 1. 25 Ordinary method 40 EXAMPLE 4 After a mixing of 1% solution of NaEX and MIBC, it was put into an atomizer and 2.0 g./ t. was added as an Aerosol to the ore pulp. Then flotation was performed under the same condition as in Example 2. The result, as shown below in Table V, was almost the same as that of Example 2 in which NaEX and MIBC were separately added as Aerosols. From this fact it is clearly proved that the matter of adding a reagent in the processes of flotation can be simplified.

In this case, the method of this invention was applied to the intermediate product of the flotation with the composition Cu0.4%, lead27%, Zn13%, and iron, FeS -19%, in order to obtain high grade refined lead ores from the product by raising the grade of lead. The conditions of the flotation were as follows:

(1) concentration of pulp-25% (2) grain size77.l% under 400 mesh (3) temperature of pulp-19 C.20 C. (4) pH-valvepH 8 For the purpose of controlling each of the 10% solution of Zn and FeS 1000 g./t. of sodalime, g./t. of sodium cyanide, and 300 g./t. of zinc sulphide were added and the condition kept for five minutes. Then 0.53 g./t. of NaEX and 0.57 g./t. of MIBC was added, as Aerosols in the same way as shown in Example 2 and the flotation was performed for three minutes.

As a result lead of grade 61.04%, and an effective gain of 52.4% were obtained. This result proved that the quantity of reinforcing and bubbling agents used were decreased approximately to and the effective gain was higher as compared with the ordinary case in which 2.5 g./t. of NaEX and MIBC are respectively employed as Aerosol; obtaining lead of grade 63.9% and an effective gain of 46.9%.

EXAMPLE 6 Refined ores were obtained at the spot of treatment as follows: copper ore: grade, Cu24.83%, grain size 92.6% under 400 mesh; lead ore: grade, Pb57.79%, grain size--94.7% under 400 mesh; zinc ore: grade, Zn 54.93%, grain size-88.5% under 400 mesh; and iron ore: grade, Fe40.54%, grain size54.2% under 400 mesh. They were respectively pretreated with mol of hydrogen-peroxide water solution and made up in a pulp having a concentration of 25%, a temperature of from 15 C.-20 C. (ambient), and a pH-valve of pH 67 (neutral). 8-9 g./t. of NaEX and the same of MIBC were added successively to the pulps and flotation was performed for seven minutes. A a result, 98.0% of Cu from the refined copper ore, 83.7% of Pb from the refined lead, 81.3% of Zn from the refined zinc ore, and 12.5% of Fe from the ferro-sulphide were floated.

From these results, in the case of this ore, lead and zinc proved to have almost the same reaction during the flotation, which permitted establishment of a plan in which better results were obtained by first separating copper only, and then lead and zinc are separated as one group by a composite flotation. -In the ordinary method, due to the fact that copper and lead have nearly the same reaction during the flotation, a preferential composite flotation for copper and lead as a group has been employed. The method of this example can thus be utilized for improving the process of separation because of the increase in the speed of flotation.

What is claimed is:

1. A method for the flotation of finely divided solids of ores, raw materials and other materials, which com prises: forming a pulp of said finely divided solid in a first liquid; feeding said pulp through an aerating zone While entraining therein a first gaseous medium and forming it into a plurality of free bubbles in said aerating zone; providing a second liquid having therein flotation reagents which are soluble or miscible with both the first and second liquids; dispersing said second liquid 10 containing the flotation reagents into a gaseous medium in the form of an Aerosol and feeding the Aerosol into said aerating zone for generating in said zone finely divided bubbles containing said Aerosol and having at the gas-liquid interface of said bubbles in said pulp a high concentration of the said flotation reagents so that the flotation reagents are preferentially and positively adsorbed onto the gas-solid interface between the bubbles and finely divided solids in the pulp for producing spontaneous coagulation of said bubbles and the finely divided solids, the coagulation of said bubbles and finely divided solids being attached to the free bubbles of the first gaseous medium produced in said aeration zone to form a.

froth; carrying out flotation of the froth; and recovering the froth and the finely divided solids therein.

References Cited UNITED STATES PATENTS 1,418,514 6/1922 Bailey 209170 X 2,316,770 4/1943 Daman 209-169 3,033,363 5/1962 Weston 209-166 X 3,202,281 8/1965 Weston 209-166 FOREIGN PATENTS 568,755 1/1933 Germany. 575,738 5/1933 Germany.

HARRY B. THORNTON, Primary Examiner R. HALPER, Assistant Examiner U.S. Cl. X.R. 209169 

